1. Field of the Invention
This invention generally relates to a new application for sound transducers. More particularly, the present invention relates to an array of flat sound transducers that provides both an omnidirectional source of sound and a highly reflective surface for projection of an image thereon.
2. Description of the Prior Art
Loud speakers may be found in a variety of settings of various scale, for example, in private homes, supermarkets, meeting rooms, concert halls, and stadiums. The prior art typically uses stereophonic reproduction when it is desirable to achieve an approximation to spatial reality in addition to both power and fidelity.
For example, in an orchestra hall or at a large outdoor concert, two powerful groups of conical speakers are usually located on either side of the performers and the stage. There are a number of problems with such an arrangement.
First, stereophonic reproduction provides a poor spatial approximation to the actual performance. The underlying goal of sound reproduction is to provide the listener with an amplified version of the performance that replicates, as nearly as possible, the musical sounds that would be heard were the listener to be located centrally in front of the stage and near enough to hear the music live from the instruments. Stereophonic reproduction falls short of this goal because by its very nature a listener is looking ahead at the performance but hearing the musical sound from either side of the stage.
Second, ordinary conical speakers are usually used in stereophonic reproduction. Because the dispersion pattern of a conical speaker is not omnidirectional but rather relatively narrow and directional (narrowing even further in proportion to frequency), listeners that are offset from the center will not hear a faithful reproduction of the live performance. In order to compensate for the relatively narrow dispersion pattern of conical speakers, the audience must extend away from the stage in a narrow lengthwise fashion in order to ensure that most listeners will be within the overlapping dispersion patterns of the two stereophonic speaker groups.
A third problem arises as a result of attempting to provide the farthest listeners with adequate volume levels. Because the power output of the speakers must be very high to reach those listeners at the rear of the lengthwise audience, listeners that are near the front are typically subject to extremely high and often painful volume levels.
A fourth problem arises in those applications where it is undesirable to have exposed speakers A good example of such an application is where the audience is also being provided with a projected visual image in addition to the audio. Such applications would for example be a movie theater or a projection screen in a meeting room. Just as with a live performers in an orchestra hall or concert situation, it is preferred to approximate spatial reality by having the audio emanate from the projected image that the viewers are observing rather than from the sides.
There are two readily apparent possibilities when attempting to hide the speakers that are being used in conjunction with a projected video image: (i) the speakers may be placed on either side of the projection screen behind screens; or (ii) the speakers may be placed behind the projection screen itself.
The first alternative is undesirable because the source of the sound is not identical with the visual image.
The second alternative has been accomplished in a number of movie theaters, although not satisfactorily so, by placing a limited array of speakers (a main central channel and two side channels) behind a perforated plastic screen. The perforations are necessary in order to allow an adequate portion of the energy being transmitted to the atmospheric molecules to pass through the screen. Such screened systems are inadequate because the perforated screen tends to limit the high frequency response of the speakers Moreover, because the perforated screen must also serve as the projection screen, the definition of the image and the percentage of reflected light is undesirably reduced. This unavoidable reduction in reflective efficiency is particularly problematic where the image is being projected under ambient light conditions.
As will be explained further herein, flat loud speakers are a desirable alternative to conical speakers Prior art flat loud speakers typically include a diaphragm that is constructed from a substantially planar panel of molded styrofoam or other suitable material The diaphragm is usually suspended from a support frame by a layer of foam rubber or the like. The front side of the diaphragm is generally smooth while the back side or frame side of the diaphragm has various shapes and channels molded therein so as to divide the panel into a plurality of regions, each region being suited for reproduction of sound in a particular frequency range. A plurality of cross members are attached to the support frame and at least one electromagnetic driver is attached thereto so that its electromagnetic coil is situated above a corresponding hammer that is attached to a predetermined region on the back side of the diaphragm.
Typical prior art flat loud speakers, methods of manufacturing the same, and components thereof are disclosed in the following prior U.S. Pat. Nos. issued to the herein inventor: 4,257,325; 4,184,563; 4,003,449; 3,801,943; 3,792,394; 3,779,336; 3,767,005; 3,722,617; and 3,596,733. The foregoing patents are hereby incorporated by reference as if fully set forth herein.